The present invention relates to drug delivery devices, in particular to transmucosal or transdermal drug delivery devices comprising a flexible backing.
Drug delivery devices for use in the present invention are designed to deliver a therapeutically effective amount of drug to the skin of a patient, e.g., to cure a skin irritation, to deliver a therapeutically effective amount of drug across the skin of a patient (transdermal drug delivery device) or across a mucous membrane of a patient (transmucosal drug delivery device). The present invention is particularly concerned with transdermal drug delivery devices but can equally well be applied to other drug delivery devices in particular transmucosal drug delivery devices. Delivery of drugs across the skin and/or mucosa avoids hepatic first-pass inactivation, poor or erratic absorption from the gastrointestinal tract, and inactivation by gastro-intestinal fluids.
Transdermal drug delivery devices typically involve a carrier (such as a liquid, gel, or solid matrix, or a pressure sensitive adhesive) into which the drug to be delivered is incorporated. Devices known to the art include reservoir type devices involving membranes that control the rate of drug release to the skin and devices involving a dispersion or solution of the drug in a matrix such as a pressure sensitive adhesive. The skin, however, presents a substantial barrier to ingress of foreign substances into the body. It is therefore often desirable or necessary to incorporate excipients into the carrier that enhance the rate at which the drug passes through the skin.
Typically the portions of the carrier that are not in contact with the skin or mucosa are covered by a backing. The backing serves to protect the carrier and the components contained in the carrier, including the drug, from the environment. It is often desirable that the backing have a relatively high vapor transmission rate, since this results in the reduction of moisture buildup on the skin beneath the device and in a corresponding reduction in the amount of skin maceration that occurs. It is also often desirable to have a conformable backing since a stiff backing may cause mechanical irritation. In order to maintain the health of the covered skin during long term wear (e.g., for periods in excess of a day), it is also desirable that the backing have a relatively high permeability to oxygen. Further, as the backing is in contact with the components of the carrier, including the drug and any excipients, it is important that the backing be stable to such components in order that the backing retains its structural integrity and conformability. It is also important that the backing not absorb the drug or excipients from the carrier. In connection with the preparation of certain reservoir type drug delivery devices, it is also desirable for the backing to be heat sealable at a relatively low temperature to a variety of other polymeric substrates.
Backings that have found use in drug delivery devices include metal foils, metalized plastic films, and single layered and multilayered polymeric films. Deficiencies that are sometimes seen with these backings include the delamination of multilayer films; the oxygen impermeability of metal foils, metalized plastic films and certain polymeric films; the low rate of moisture vapor transmission of metal foils, metalized plastic films and certain polymeric films; undue stiffness and lack of conformability of metal foils, metalized plastic films and certain polymeric films; instability of certain polymeric materials to the components of the carrier; and absorption of components from the carrier by certain polymeric materials. Accordingly, there is a substantial need for a backing material that addresses some or all of the above problems.